PRINCIPLES AND APPLICATION OF THE

ISCST3 GAUSSIAN MODEL FOR

POLLUTANTS TRANSPORT SIMULATION

(Abstract of Alvaro Romero Moralís Graduation Project,

November 1998)

__________________________________________







1.- INTRODUCTION
 
 

2.- THE ISCST3 MODEL
 
 

3.- THE IMW INTERFACE
 
 

4.- THE IMXW INTERFACE
 
 

5.- SIMULATION RESULTS ANALYSIS
 
 

6.- CONCLUSIONS AND FUTURE DEVELOPMENTS

_______________________________________________________________









1.- INTRODUCTION
 
 

This project pursuits the following four main objectives:
 
 

    1. Assure the maintenance of the IMW (ISCST3 Manager for Windows 95) interface, a program developed by the Environmental Software and Modelling Group which is now installed in a petrol refinery located in La Coruña, Spain. ISCST3 was chosen because of its capacity of supplying pollutant concentration data easily, fast and accurately.

    2.  

       
       
       
       
       
       
       
       
       
       
       

    3. The development of a new version of IMW, with new features from the ISCST3 model, to be installed in a cement factory located near of Bilbao, Spain. The maintenance of this version of IMW must be assured too.

    4.  

       
       
       
       
       
       
       
       
       
       
       

    5. The development, as part of my graduation project, of IMXW (ISCST3 Manager for X-Windows), a new interface for the ISCST3 model which should work under UNIX environment.

    6.  

       
       
       
       
       
       
       
       
       
       
       

    7. A brief analysis of several simulations executed under both IMW and IMXW.

 
 

2.- THE ISCST3 MODEL
 
 

ISCST3 (Industrial Source Complex Shot-Term Model 3) is a Gaussian Transport Model developed by the U.S. E.P.A. (United States Environmental Protection Agency).
 
 

Transport Models are the centre of Air Quality Models. In fact, a Transport Model is the part of an Air Quality Model that calculates the pollutants dispersion across the atmosphere starting from meteorological and emissions data supplied by other models.
 
 

The Gaussian Model is a particular kind of Transport Model developed in the 70´s. The principle of the Gaussian Model is the statistic normal distribution, which is used to represent the dispersion of a pollutants plume emitted from a point source.

The normal distribution





The mean part of the plume will follow a single direction, but part of its concentration will be dispersed in both the horizontally and vertically according to two standard deviations. This standard deviations raise as the plume moves away from its emission source.

Standard deviations of the plume

This is the Gaussian Model analytic formula that calculates the concentration of a pollutant in one point (r) owed to an emission at s:

where: (if d£ 0 then C=0 in (1)). ISCST3 implements, in FORTRAN language, the Gaussian Model including several extensions: pollutants reflection, wet and dry deposition, building and stack downwash, simulation of area, volume and open pit emission sources, simulation of complex terrain, and so on.
 
 

ISCST3 is driven by an ASCII control file that contains all the information about a simulation. This control file is structured in six different sections:
 
 

    1. Control options. In this section, the user must include the general options of the simulation.
    2. Source options. In this section, the user must include all the emission sources and its characteristics. Emission can be both constant or variable, in which case the user must specify the path of an emissions file.
    3. Receptors options. In this section, the user must include a virtual pollutant receptor points net.
    4. Meteorological options. In this section, the user must include the path of the file that contains the meteorological data for the simulation period.
    5. Terrain options. In this section, the user must include the path of a file that contains the altimetry of the simulation domain.
    6. Output options. In this section, the user must specify the desired characteristics for the output files.
The model results a file that contains the pollutant concentration in all the receptors specified on the fourth section accumulated during the simulation period. 3.- THE IMW INTERFACE
 
 

IMW welcome screen







The IMW interface is a friendly-user way to build an ISCST3 control file implemented in Microsoft Visual Basic 4.0 for Windows 95.
 
 

IMW easily allows the user to specify the parameters required on the six sections of a control file. The user can save control files and open them later in order to run a ISCST3 simulation.
 
 

When a simulation has been executed, IMW automatically calls the Golden Software program called SURFER and displays a graphic visualization of its results over both a surface and a contour map of the considered simulation domain. Concentration data of the ISCST3 output file is interpolated using the kriging method in order to be displayed.
 
 

IMW features two data preprocessors in order to easily transform the crude data coming from sensors located at the factories in structured data ready to be accepted by ISCST3:
 
 

    1. A meteorological data preprocessor, programmed in FORTRAN, that averages the crude data and calculates the Pasquill-Gifford atmospheric stability category and the mixing height at every simulation hour.
    2. An emissions data preprocessor, programmed in Turbo Pascal, that averages the crude data and transforms its units into g/s.
Moreover, IMW incorporates the E.P.A. program B.P.I.P. (Building Profile Input Program) that calculates, starting from the buildings surrounding the emission sources characteristics, the necessary input parameters to ISCST3 in order to simulate the building downwash effect.  
 
4.- THE IMXW INTERFACE
 
 

IMXW welcome screen







The IMXW interface is a friendly-user way to build an ISCST3 control file implemented in Tcl/Tk for UNIX plataforms.
 
 

IMXW using way is very similar to IMWís, and features the same ISCST3 characteristics.
 
 

IMXW incorporates B.P.I.P. and the meteorological and emissions preprocessors. B.P.I.P. and the meteorological preprocessor have been re-compiled in order to run under UNIX, and the emission preprocessor has been re-programmed in C.
 
 

IMXW still havenít a visualization tool in order to display the ISCST3 simulation results. This is a future development of this project (see point 6).
 
 
 
 
 
 
 
 
 
 

5.- SIMULATION RESULTS ANALYSIS
 
 

Several simulations have been execute through IMW and IMXW in order to test them. As an example of them, here you can see a comparison between a simulation in which the building downwash effect has been considered (simulation I) and another identical simulation without considering that effect (simulation II). The chosen simulation date is 1998-07-07.
 
 

The simulated pollutant is SO2. The domain terrain is complex and rural. Two puntual sources are simulated, with identical constant emission rate of 10 g/s. Both sources are 55 meters high.
 
 

                                                      Simulation I (24 hours)                                  Simulation II (24 hours)
 
 
 
 
 
 
 
 
 
 
 
 

Comparative graphic
 
 

Another simulations have been made in order to try to validate the model results. This try consists of compare the concentration data supplied by the model with available inmission data recovered on a meteorological station near to the emission sources simulated.

Simulation III (24 hours)
 
HOUR
1
2
3
4
5
6
7
8
9
10
11
12
Inmission
24
23
22
24
19
19
19
20
22
29
42
43
Concentr.
0
12.4
12.4
12.4
0.03
0
0
0
0
0
0
0

 
  Inmission/concentration comparation (1 to 12 hours)
 
HOUR
13
14
15
16
17
18
19
20
21
22
23
24
Inmission
60
51
48
81
83
67
50
49
45
38
33
33
Concentr.
0
6.56
6.30
3.50
5.16
3.27
3.72
29.53
0.0077
0
0
0

 
  Inmission/concentration comparation (13 to 24 hours) The inmission data is always higher than the concentration data supplied by the model. This is owed to the fact that there are other sources that havenít been considered in the simulation and that contribute to form the final recovered inmission data.
 
 

6.- CONCLUSIONS AND FUTURE DEVELOPMENTS
 
 

This projectís conclusions can be resumed in the achievement of the objectives enumerated in the Introduction.

  1. Maintenance of the IMW (ISCST3 Manager for Windows 95) interface installed in La Coruña has been carried out.

  2.  

     
     
     
     
     
     
     
     
     
     
     

  3. The new version of IMW has been developed and installed in Bilbao successfully. The maintenance of this version of IMW has been carried out too.

  4.  

     
     
     
     
     
     
     
     
     
     
     

  5. IMXW (ISCST3 Manager for X-Windows), a new interface for the ISCST3 model that works in a UNIX environment, has been developed successfully.

  6.  

     
     
     
     
     
     
     
     
     
     
     

  7. Several simulations have been executed under both IMW and IMXW in order to test the interfaces. The results of this simulations have been analysed to prove that they accord to the known theory about the Gaussian Model. Besides, a try of model results validation has been done.
Some of the possible future developments for this project are:
  1. Include in IMW and IMXW non-considered features of the ISCST3 model like the wet deposition, the radioactive pollutants, the area, volume and open pit sources and so on.

  2.  

     
     
     
     
     
     
     
     
     
     
     

  3. IMXW was developed in Tcl/Tk in order to make it compatible with the EMMA application from the Environmental Software and Modelling Group. EMMA is an Eulerian Transport Model based in numerical methods. The simulation domain is gridded, and the model results a single pollutant concentration data for every single cell of the grid. Nesting a Gaussian Model (for example, ISCST3, using IMXW) in some user desired cells will provide the user the pollutant concentration in all the points of that cell.

  4.  

     
     
     
     
     
     
     
     
     
     
     

  5. IMXW still needs visualization tool in order to display graphically the ISCST3 results.

  6.  

     
     
     
     
     
     
     
     
     
     
     

  7. IMW and IMXW would be provided of a tool to compare, in all the simulation domain points, interpolated (for example, with the kriging method) inmission data with the concentration data calculated by the model in order to validate it. This tool should be used to determine one sourceís responsability in the total concentration amount.